Xylitol, ribitol and d-arabitol can be utilized by certain strains of Lactobacillus casei and Streptococcus avium via a pathway unique to these microorganisms. The pentitols eventually enter the pathway of pentose metabolism and the ensuing heterofermentation of the sugar alcohols results in the production of lactate, acetate and ethanol. Regulation by glucose is not stringent and several of the enzymes involved in pentitol dissimilation continue to be synthesized while glucose is metabolized. Gram negative isolates from subgingival plaque deposits have been characterized as cytophaga sp. These bacteria selectively colonize the root surfaces of teeth, softening and demineralizing the root structure in the process. The initial attachment of the organism to hydroxylapatite appear to be mediated by certain protein and lipid components of the cell's outer membrane.